The evolution of multicomponent systems at high pressures Part IV. The genesis of optical activity in high-density,abiotic fluids

摘要

A thermodynamic argument has been developed which relates the chirality of the constituents of a mixture of enantiomers t~ th. system excess volume, and thereby to its Gibbs free enthalpy. A specific connection is shown between the excess volume and, the statistical mechanical partition function. The K.ihara-Steiner equations, which describe the geometry of convex hard bodies, have been extended to include also chiral hard bodies. These results have been incorporated into an extension of the Pavli~ek—Nezbeda—Boublik equation of state fot convex, aspherical, hard-body systems. The Gibbs free enthalpy has been calculated, both for single-component and racemic mixtures, for a wide variety of hard-body systems of diverse volumes and degrees of asphericity, prolateness, and chirality. The results show that a system of chiralenantiomers can evolve to an unbalanced, scalemic mixture, which must manifest optical activity, in many circumstances of density, particle volume~asphericity, and degree of chirality. The real chiral moleculesfluorochoroiodomethane,CHFCII,and4-vinylcyclohexene, C5H12, have been investigated by Monte Carlo simulation, and observed to both manifest positive excess volumes (in their racemic mixtures) which increase with pressure, and thereby the racemic - scalemic transition to unbalanced distributions of enantiomers. The racemic-scalemic transition, responsible for the evolution of an optically active fluid, is shown to be one particular case of the general, complex phase behavior characteristic of “closely-similar” molecules (either chiral or achiral) at high pressures.